The invention relates to a cooling system as well as a method for cooling thermally stressed housings or housing parts in turbo-machines, in particular in a turbine.
In order to cool a housing or housing parts of a turbo-machine, in particular that of a turbine, feeder air, which is usually sucked in from the area around the housing, is fed into the housing. When flowing through the housing, this air is then heated and is removed from the housing as waste air. For this purpose, a conventional cooling system has a feeder air line that connects a feeder air connection of the housing with an area around the housing in order to feed the feeder air through the feeder air line into the housing. Also provided is a waste air line that is connected with a waste air connection of the housing in order to remove the waste air heated by the housing. A fan that circulates the cooling air flow is positioned inside the feeder air line. In order to influence the cooling performance of such a cooling system, it is known to change the speed of the fan, for example by means of a gear. In the same way, the use of closing elements, such as, for example, butterfly valves, gate valves, or shutter-type valves, are known, with which the cooling air flow or parts thereof can be influenced or locked out. By means of these measures, the air volume fed into the housing for cooling, i.e. the feeder air volume, is therefore adjusted in order to change the cooling performance of the cooling system.
In order for the cooling of the housing to be able to function properly, clear and reproducible flow conditions must exist during the flow through the housing. This is only possible, however, if the added feeder air does not vary too much from a cooling air volume on which the design of the cooling system is based. This means that only a relatively small adjustment range is available for changing the feeder air volume. Furthermore, a temperature gradient that may result in undesired tensions in the housing forms along the flow path within the housing.
The invention intends to remedy this. The invention at hand relates to the objective of disclosing an embodiment for a cooling system or respectively for a method of the initially mentioned type, which enables an adjustment of the cooling performance within a relatively large range. In addition, a possibility for reducing the temperature gradient along the flow path in the housing should be disclosed.
The invention is based on the general idea of changing the cooling performance by way of the temperature of the added feeder air. In order to make it possible for the flow conditions to remain principally unchanged during the flow through the housing, the cooling performance of the cooling system can be adjusted by changing the feeder air temperature within a very large range. With an increase in the temperature of the feeder, it is also possible to reduce the temperature gradient forming along the flow path in the housing, so that undesired tensions in the housing are reduced or avoided.
The means for changing the feeder temperature may comprise, for example, an appropriate heating device and/or cooling device that may be positioned upstream or downstream from the fan in the feeder air line. Such a cooling and/or heating device can also be integrated in the fan.
However, preferred is an embodiment in which the means for changing the feeder air temperature comprise a recirculated air line that connects the feeder air line upstream from the fan with the waste air line, whereby an adjustable recirculated air lock-out element is positioned in this recirculated air line. In this embodiment, the feeder air temperature is changed by mixing more or less waste air with the feeder air. The more waste air is mixed with the feeder air, the higher the feeder air temperature is. A crucial advantage of this embodiment is that the increase of the feeder air temperature does not increase additional energy, since the required heat is removed from the waste air. Such an embodiment can also be realized at relatively low cost.
In a useful further development, the fan may be constructed so that the air volume circulated by the fan is adjustable. The actually known measure for changing the cooling performance is hereby combined with the measure according to the invention that acts in the same way, resulting in additional adjustment possibilities.
In a further embodiment, an adjustable waste air closing element may be positioned in the waste air line downstream from the recirculated air line. Alternatively, or additionally, an adjustable feeder air closing element may be positioned in the feeder air line upstream from the recirculated air line. This means that the recirculated air closing element is open and the waste air closing element is closed and/or the feeder air closing element is closed, a purely recirculated air operating mode can be set, during which the cooling performance is obtained essentially through leaks or convection heat emission.
Here also, the invention is based on the general idea of influencing the cooling performance via the feeder air temperature.
Other important characteristics and advantages of the invention are found in the secondary claims, the drawing, and the related description of the drawing,